This invention relates to transporting electron beams without disturbance, and more particularly to a means of transporting an electron beam across magnetic field lines without adding much perpendicular velocity to the electrons.
Presently, there is substantial interest in increasing the electrical current limits of the conventional betatron. Several of these new approaches require at least a large toroidal magnetic field for the higher circulating currents and still require an inductive electric field for electron acceleration.
In the conventional betatron, electron production or injection is done inside the toroidal vacuum chamber. With this conventional injection technique a very large injection energy (greater than or equal to one Mev) is required in order to achieve the desired current levels (several kiloamperes). There are three problems with high energy internal injection. First, it requires a large opening in the torus, which introduces large electric and magnetic field perturbations and consequently disturbs the circulating electron beam. Second, the electron beam producing diode produces gases and plasma which can have adverse effects on the beam. Finally, it requires an injector with a short fall time pulse to avoid perturbing the beam after the first revolution.
To avoid the difficulties of internal injection the electron producing diode must be located external to the vacuum chamber (external injection). The difficulty with external injection is that the electron beam must now cross magnetic field lines without disturbing the electrons and specifically without adding perpendicular velocity to the electrons. Prior means for transporting electron beams across field lines are; 1) electrostatically charged and current driven axial wires, 2) exploding wire channels, 3) laser in itiated current driven channels, 4) magnetically shielded channels and 5) Z-pinch, channels. These schemes provide a means for electron beam transport, however, they all substantially perturb the electrons either during transport in the injector or when the electrons are circulating in the torus. Approach 4 is the only scheme that substantially perturbs the electrons in the torus.